Brightness control for auto-focus in an optical system

ABSTRACT

An imaging device includes an image lens, an image sensor, and a brightness control element. The imaging device receives an image through the image lens in the optical pathway and detects the image at the image sensor. Brightness of the light impinging on the image sensor is adjusted using the brightness control element. In one automatic focus technique, the brightness control element controls luminous flux diameter. In another automatic focus technique, the brightness control element controls light transmittance without changing the luminous flux diameter. During detection of the auto-focus (AF) signal for a bright image, a brightness controller leaves the luminous flux diameter open and inserts a neutral-density (ND) filter into the optical path to avoid saturation of the signal from the image sensor. When the neutral density filter is inserted, an auto-focus controller moves the focusing lens to the best focus position independent of the auto-focus (AF) and an automatic-exposure (AE) signals. When the image is focused, the appropriate aperture diameter (F number) is inserted based on the automatic-exposure signal.

CROSS-REFERENCE

[0001] The present invention is related to subject matter disclosed in the following co-pending patent applications:

[0002] 1. United States patent application entitled, “Zoom and Focus Control Method and System” (HP Docket No. 10006921-1), naming Michelle Ogg, Gregory V. Hofer, and David K. Campbell as inventors and filed on even date herewith; and

[0003] 2. United States patent application entitled, “Zoom and Focus Control System in an Optical System” (HP Docket No. 10006923-1), naming Gregory V. Hofer, David K. Campbell, Masahiro Ohno, and Yoshihiro Yamazaki as inventors and filed on even date herewith.

BACKGROUND OF THE INVENTION

[0004] Electronic imaging devices such as electronic cameras and digital cameras acquire and record images using an electrical image sensor. Usage of an electrical image sensor permits beneficial functionality such as automatic focusing. For example, a digital camera can use the signal from the electrical image sensor to detect characteristics of light within the optical path of the camera. The automatic focus operation involves analysis of the spatial distribution of the light impinging on the detector, and the intensity of light at the various positions in the spatial field. Analysis of the light distribution can be used to create an auto-focus signal and the auto-focus signal can be used to adjust the position of an image lens to a focus position, thereby adjusting the focus.

[0005] An optimum signal for properly and effectively focusing is a signal that is easily detected by sensing circuitry. Control circuits generally use various triggering techniques to determine whether conditions are proper for actuating a control signal. For example, a trigger signal is often used to detect some system characteristic. In the case of an automatic focusing operation, what is desired is a signal that precisely determines whether an image is in focus.

[0006] Fidelity of the automatic focus signal depends largely on the lens F number, which corresponds to the amount of light entering the optical path of the camera. When the optical aperture of the camera is closed, the electrical image sensor detects a signal that is spread uniformly over the two-dimensional surface of the sensor. The focal depth is great and the small differences between detected signal at different spatial positions does not permit fine detection of the focused condition. When the aperture is open, the focus condition is more easily detected because the depth of focus is much shallower. Thus an open aperture is highly advantageous for detecting a suitable auto-focus signal. However, if a bright image is detected, for example such as occurs in a highly reflective condition such as a ski slope scene with bright sun, then the brightness may overflow the range of the electrical image sensor. The brightness causes the sensor to saturate, making detection of a suitable auto-focus signal difficult.

[0007] An automatic focus camera typically adjusts the brightness control by changing the electrical shutter speed of the camera. In very bright conditions brightness control by modification of shutter speed is difficult to control.

SUMMARY OF THE INVENTION

[0008] What is needed is an automatic focus device that accurately determines a focus condition without decreasing the automatic focusing accuracy even for bright objects in the image field.

[0009] In accordance with an aspect of the present invention, an imaging device includes an image lens, an image sensor, and a brightness control element. The imaging device receives an image through the image lens in the optical pathway and detects the image at the image sensor. Brightness of the light impinging on the image sensor is adjusted using the brightness control element. In one automatic focus technique, the brightness control element controls luminous flux diameter. In another automatic focus technique, the brightness control element controls light transmittance without changing the luminous flux diameter. During detection of the auto-focus (AF) signal for a bright image, a brightness controller leaves the luminous flux diameter open and inserts a neutral-density (ND) filter into the optical path to avoid saturation of the signal from the image sensor. When the neutral density filter is inserted, an auto-focus controller moves the focusing lens to the best focus position independent of the auto-focus (AF) and an automatic-exposure (AE) signals. When the image is focused, the appropriate aperture diameter (F number) is inserted based on the automatic-exposure signal.

[0010] In accordance with an embodiment of the present invention, an imaging device includes an image lens disposed in an optical path, an image sensor coupled to the optical path and capable of detecting illumination passing through the image lens and generating an image signal based on the detected illumination, and a brightness controller coupled along the optical path. The brightness controller is capable of executing an auto-focus operation that generates an auto-focus signal based on the image signal and a brightness control operation that controls luminous flux diameter along the optical path. A light transmittance control operation controls light transmittance without changing the luminous flux diameter. The auto-focus operation determines a focus condition without changing the luminous flux diameter.

[0011] In accordance with another embodiment of the present invention, a control process is executable in an imaging device that includes an imaging lens disposed in an optical path, an image sensor coupled to the optical path, and a brightness controller. The image sensor is capable of detecting illumination passing through the image lens and generating an image signal based on the detected illumination. The control process includes a processing logic capable of executing an auto-focus operation, a processing logic capable of executing a brightness control operation, and a processing logic capable of executing a light transmittance control operation. The auto-focus operation generates an auto-focus signal based on the image signal. The brightness control operation controls luminous flux diameter along the optical path. The light transmittance control operation controls light transmittance without changing the luminous flux diameter, the auto-focus operation determining a focus condition without changing the luminous flux diameter.

[0012] The described automatic focusing operation and apparatus attain a highly suitable focus result for images with a wide range of brightness without decreasing the auto-focus accuracy.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013]FIG. 1 is a schematic block diagram that illustrates an electronic imaging device that is suitable for implementing a brightness and auto-focus control system in accordance with an embodiment of the present invention.

[0014]FIG. 2 is a simplified, highly schematic pictorial diagram that depicts an optical path of an imaging device in accordance with an embodiment of the present invention.

[0015]FIG. 3 is a signal intensity graph showing an auto-focus signal which is indicative of the intensity of light sensed at the image sensor for a range of positions of the focus lens.

[0016]FIG. 4 is a schematic flow chart illustrating an automatic focus technique for usage in an imaging device.

[0017]FIG. 5 is a schematic block diagram that illustrates another electronic camera also suitable for implementing a brightness and auto-focus control system in accordance with an alternative embodiment of the present invention.

DESCRIPTION OF THE EMBODIMENT(S)

[0018] Referring to FIG. 1, a schematic block diagram illustrates an electronic camera 102 that is also suitable for implementing a zoom and focus control system 100 in accordance with an alternative embodiment of the present invention. A sensor such as a charge-coupled device (CCD) photo sensor 104 that detects light passing through a lens system 106 to form an image. The alternative illustrative zoom and focus control system 100 has a lens system 106 that also includes a plurality of lens groups, each of which includes one or more lenses. The present example also has three lens groups, first lens group 108, second lens group 110, and third lens group 112. The first lens group 108 is a fixed-objective lens. The second lens group 110 is a moving group lens that contains an aperture stop (not shown). The second lens group 110 moves in conjunction with the third lens group 112 to cause magnification to change when the lens system 106 moves. THE second lens group 110 moves in a nonlinear manner to hold the image plane in a relatively constant position as the lens system 106 is zoomed. The second lens group 110 is also moved to focus the lens system 106 after reaching a particular focal length. The third lens group 112 is also a moving group of lenses in the lens system 106. The third lens group 112 is also a moving lens group. The third lens group 112 moves in a linear manner to change the focal length of the camera as the lens zooms.

[0019] The CCD photo sensor 104 is a two-dimensional array of charge-coupled photo sensors that captures an image focused onto the photo sensors by the lens system 106. Individual photo sensor sites are pixels with an associated color such as red, green, or blue. CCD photo sensor 104 is exposed to light and charge integrates at the individual pixel site proportional to the number of photons received at the site. Clock drivers 114 are connected to the CCD photo sensor 104 and convey clock signals to control the read-out process of CCD photo sensor 104. Image processing hardware (not shown) generates the clock signals and sends the clock signals from the image processing hardware through the clock drivers 114 to the CCD photo sensor 104. The clock drivers 114 supply clock signals with high current and sufficient frequencies to drive highly capacitive CCD control lines.

[0020] A low pass filter 116 is connected to the CCD photo sensor 104 for anti-alias filtering to avoid optical moire effects resulting from the discrete CCD pixel structure. An example of the low pass filter 116 includes two birefringent quartz plates (not shown) and a quarter-wave plate (not shown). One birefringent quart plate produces filtering with respect to a horizontal direction of the CCD array. The other birefringent plate filters in a vertical direction of the CCD array. The quarter-wave plate functions is a depolarizer. The term low-pass filter indicates imaging of only a low spatial frequency image.

[0021] The CCD photo sensor 104 generates image signals and passes the signals through an analog to digital converter (ADC) 118 to the image processing hardware. Row-by-row pixel image data from the CCD photo sensor 104 are an analog voltage passed to the analog to digital converter 118. The analog to digital converter 118 amplifies and digitizes the image signal. The digitization process generates an N-bit digital word for each pixel. The analog to digital converter 118 clocks pixel data into the image processing hardware.

[0022] A shutter/aperture module 120 is interposed between the second lens group 108 and the third lens group 110. The shutter/aperture module 120 includes a shutter 122, apertures 124, and a neutral density filter 126. The shutter 122 is a blade switched into the optical path 128 of the lens system 106 to prevent light from reaching the CCD photo sensor 104. The shutter 122 blocks light at the end of an exposure time to complete image capture and when the camera is powered off to protect the CCD photo sensor 104 from receiving excessive light and damaging individual sensor elements.

[0023] The apertures 124 are multiple blades, each containing a hole. Different blades typically have different diameter holes. Different apertures can be switched into the optical path 128 to reduce the light transmitted through the lens system 106 to the CCD photo sensor 104. Different apertures 124 are used to control light exposure and focus depth of field. A typical still-image electronic camera has one or two aperture blades. In other designs, the aperture 124 may be composed of a diaphragm with continuously variable aperture hole sizes to supply a greater number of selectable apertures.

[0024] The neutral density filter 126 is an additional blade that can be switched into the optical path 128. The neutral density filter 126 also reduces the light passed through the lens system 106 to the CCD photo sensor 104. The aperture 124 and the neutral density filter 126 function similarly, but differ in that the neutral density filter 126 can be used to reduce the amount of light passing through the lens system 106 without affecting the focus depth of field. In contrast, usage of an aperture to reduce light to the CCD photo sensor 104 changes the depth of focus. The neutral density filter 126 can be used in conjunction with the apertures 124 to further reduce the level of light passing to the CCD photo sensor 104.

[0025] The shutter/aperture module 120 is controlled by signals passed from a camera control element (not shown) via solenoids 130. Individual blades of the shutter 122, the apertures 124, and the neutral density filter 126 are actuated in and out of the lens optical path 128 by a plurality of solenoids including a shutter solenoid 129, an aperture solenoid 130, and a neutral density filter solenoid 131. The solenoids are driven by coil drivers 132 which supply voltage and current for actuating the blades into position in a timely manner. The coil drivers 132 are controlled by signals from a processor (not shown) such as a central processing unit (CPU), a microcontroller, or control logic. The camera control element may be software or firmware that executes on the processor.

[0026] The processor determines relative positioning of the second lens group 110, and the third lens group 112, thus controlling zoom and focus functionality. The processor executes application programs that supply control information to a motor driver 134, an executing program code supplying control signals to a first stepper motor 138 and a second stepper motor 140. The stepper motors 138 and 140 physically control the position of the second lens group 110 and the third lens group 112, respectively.

[0027] In the illustrative electronic camera 102, the motor driver 134 sends signals to the stepper motor 138 that is connected to the second lens group 110 by gear reduction 150 and a lead screw 152. Similarly, the motor driver 134 sends signals to the stepper motor 138 that is connected to the third lens group 112 also by gear reduction 150 and a lead screw 152. The stepper motors 138 and 140 receive signals from the processor via the motor driver 134 that determine the position and motion of the second lens group 110 and the third lens group 112. In alternative systems, other types of motors and drive mechanisms can be used to controls lens position adjustment of the second and third lens groups 110 and 112. Photo sensors 154 are connected to the motor and drive mechanism for the second and third lens groups 110 and 112 to monitor positioning of the lens groups 110 and 112. The processor determines the initial positions of the second and third lens groups 110 and 112 by moving the lens groups toward the photo sensors 154 and detecting when flag 156 mounted on the second and third lens groups 110 and 112 reaches the photo sensors 154. The position at which the photo sensors 154 detect the flags is a home position. The processor measures the positions of the second and third lens groups 110 and 112 relative to the home position. The processor tracks the number of steps the stepper motors 138 and 140 execute in all moves relative to the home position.

[0028] The motor drivers 134 supply voltage and current to the stepper motors 138 and 140, thus determining the position and motion of the second lens group 110 and the third lens group 112. The motor drivers 134 are controlled by signals from the processor.

[0029] Referring to FIG. 2, a simplified, highly schematic pictorial diagram depicts an optical path 202 of an imaging device 200 in accordance with an embodiment of the present invention. Arranged along an optical axis 204 are an image lens 206, a neutral density filter 208, an aperture 209, a focus lens 210, and an image sensor 212. The simplified diagram is used for illustrative purposes and omits additional components such as additional lenses, for example a zoom lens that may be included in some devices. The image lens 206 and focus lens 210 may be single lenses or compound lenses. When the aperture 209 is open, light passes along the optical path 202 to the image sensor 212, a two-dimensional array of sensor elements.

[0030] Referring to FIG. 3 in conjunction with FIG. 2, a signal intensity graph depicts an auto-focus signal 300 which is indicative of the intensity of light sensed at the image sensor 212 for a range of positions of the focus lens 210. The focus lens 210 scans under control of a focus control element (not shown) in the imaging device 200 from a position adjacent the aperture 209 through a range of focus lens positions toward the image sensor 212. The illumination signal as a function of focus lens position is called an auto-focus (AF) signal and is used to focus the imaging device 200.

[0031] When the aperture 209 is closed, the illumination detected by the image sensor 212 is relatively low in intensity and is generally distributed across the range of focus lens positions. For the closed aperture, so that the AF signal 302 at a focus position does not greatly exceed the amplitude when the image is not in focus. Automatic focusing control is typically implemented using electronic circuits that detect a suitable indication of a focused condition and control positioning of pertinent components such as the focus lens 210 to acquire images in the focused condition. Generally, triggering circuits are used to monitor the AF signal and detect suitable focus conditions. Various aspects of the AF signal may be used to determine the focused condition. A peak detector may be used to detect the maximum AF signal although the closed-aperture AF signal 302 does not greatly differ across the range of focus lens positions so that proper focusing is difficult to achieve. Peak detection is highly sensitive to noise, increasing the difficulty in attaining a focused condition. Other aspects of the AF signal may be monitored to determine the focus condition, such as the slope of the AF signal. The closed-aperture AF signal 302 has a small slope, or derivative, signal throughout the focus position range so that facility of detection is not greatly improved over peak detection.

[0032] When the aperture 209 is open, the illumination signal detected by the image sensor 212 is relatively high in intensity near the focus position of the focus lens 210 and low outside a suitable focus region. A wide aperture thus results in a narrow field for the open-aperture AF signal 304. The open-aperture auto-focus signal 304 is therefore highly preferable over the closed-aperture AF signal 302 for detecting a focused condition. Both peak detection and slope detection are facilitated by usage of the open-aperture AF signal 304 to detect a focused condition. The problem with usage of the open-aperture AF signal 304 for detecting a focused condition is that the AF signal can be saturated due to high illumination, creating drop-outs and noise that obscure the focused condition.

[0033] The illustrative imaging device 200 improves auto-focus capabilities by using the neutral density filter 208 to reduce the level of illumination detected by the image sensor 212 so that the open-aperture AF signal 304 can be used to determine a focused condition. Accordingly, the imaging device 200 detects the auto-focus signal by maintaining the aperture 209 at a desired preselected setting and reducing light intensity detected by the image sensor 212 through usage of the neutral density filter 208. The user sets the imaging device 200 to acquire images at a selected aperture setting, or F number, and monitors the AF signal while the F number is maintained at the same setting, thereby maintaining the same luminous flux diameter. The neutral density filter 208 is inserted while the AF signal is monitored so that the AF signal has reduced or removed distortion from saturation effects. Usage of the neutral density filter 208 controls the amount of light to reach the image sensor 212 without changing the aperture 209 setting. In the illustrative example, the neutral density filter 208 appears to reduce the intensity of incident light on the image sensor 212 at an amount that approximates the light reduction of changing the aperture setting by two F stops.

[0034] Referring to FIG. 4, a schematic flow chart illustrates an automatic focus technique 400 for usage in an imaging device. The automatic focus technique 400 can be executed as a firmware or software program or routine in a processor connected to an imaging system such as the systems shown in FIGS. 1, 2, and 5. Alternatively, the automatic focus technique 400 can be performed in a controller or logic circuit. In a typical application, the automatic focus technique 400 can operate continuously in response to various signals produced by the imaging system, timing elements (not shown), and the processor.

[0035] In a detect illumination operation 402, the image sensor detects illumination at the sensor elements and produces a signal indicative of the amount of light impinging on the sensor elements. The detected illumination level is used to generate an automatic-exposure (AE) signal as well as the AF signal. If the amount of detected light is increased, according to logic block 404, the neutral density filter is interposed 406 into the optical path to reduce the detected light to a level within a desired range. In response to any changes in system settings 408, the imaging device performs various zoom 410, auto-exposure 412, and auto-focus 414 tasks. Generally the zoom task 410 changes the position of a zoom lens to a desired position. The auto-exposure task 412 modifies the illumination level of light reaching the image sensor in some circumstances by changing the aperture in other circumstances by inserting the neutral density filter into the optical path. The auto-focus task 414 modifies the position of a focusing lens and detects the AF signal at different positions. The auto-focus task 414 detects a desired AF signal condition, for example the maximum AF signal or the maximum slope AF signal, and determines that a suitable position of the focus lens on that basis.

[0036] Although in the illustrative examples, the second and third lenses are used for zooming and the second lens is used for focus. In other embodiments, the lenses may be used in a different manner. For example, the first and second lens groups may be used for zooming and the third lens group used for focusing.

[0037] Referring to FIG. 5, a schematic block diagram illustrates another electronic camera 502 that is suitable for implementing a zoom and focus control system 500 in accordance with an embodiment of the present invention. An image is detected at a sensor, for example a charge-coupled device (CCD) photo sensor 504 that detects light passing through a lens system 506. In the illustrative zoom and focus control system 500, the lens system 506 includes a plurality of lens groups, each of which includes one or more lenses. One example has three lens groups, first lens group 508, second lens group 510, and third lens group 512. The second lens group 510, termed a variator, changes the effective focal length of the lens and moves in a linear manner. The first lens group 508 moves in a nonlinear manner relative to the linear motion of the second lens group 510 and functions as a compensator. The first lens group 508 functions to hold the image plane relatively constant as the lens is zoomed over the range of focal lengths of the lens system 506. The third lens group 512 is a positive is a positive element that is moved to focus the lens system 506.

[0038] The CCD photo sensor 504 is a two-dimensional array of charge-coupled photo sensors used to capture the image that is focused onto the photo sensors by the lens system 506. The individual photo sensor sites are defined as pixels and have an associated color such as red, green, or blue. As the CCD photo sensor 504 is exposed to light, charge integrates at the individual pixel site proportional to the number of photons received at the site. Clock drivers 514 are connected to the CCD photo sensor 504 and propagate clock signals that are used to control the read-out process of the CCD photo sensor 504. Image processing hardware (not shown) generates the clock signals. The clock signals propagate from the image processing hardware through the clock drivers 514 to the CCD photo sensor 504. The clock drivers 514 supply clock signals with high levels of current at sufficient frequencies to drive highly capacitive CCD control lines.

[0039] A low pass filter 516 is connected to the CCD photo sensor 504 for usage as an anti-aliasing filter to avoid optical moire effects that occur due to the discrete nature of the CCD pixel structure. One suitable example of the low pass filter 516 includes two birefringent quartz plates (not shown) and a quarter-wave plate (not shown). One of the birefringent quart plates produces filtering with respect to a horizontal direction of the CCD array. The second birefringent plate produces filtering in a vertical direction of the CCD array, 90° shifted from the horizontal direction. The quarter-wave plate functions as a depolarizer. The term low-pass filter indicates imaging of only a low spatial frequency image.

[0040] The CCD photo sensor 504 generates image signals that are passed through an analog to digital converter (ADC) 518 to the image processing hardware. Row-by-row pixel image data is read from the CCD photo sensor 504 as an analog voltage and is passed to the analog to digital converter 518. The analog to digital converter 518 amplifies and digitizes the image signal. The digitization process generates an N-bit digital word for each pixel. The analog to digital converter 518 clocks the digital words for the pixels into the image processing hardware.

[0041] A shutter/aperture module 520 is interposed between the first lens group 508 and the second lens group 510. The shutter/aperture module 520 includes a shutter 522, apertures 524, and a neutral density filter 526. The shutter 522 is a blade that is switched into the optical path 528 of the lens system 506 to prevent light from reaching the CCD photo sensor 504. The shutter 522 typically is controlled to block the light at the end of an exposure time to complete image capture. The shutter 522 is also closed when the camera is powered off to protect the CCD photo sensor 504 from receiving excessive light, potentially causing damage to the individual sensor elements.

[0042] The apertures 524 are multiple blades containing different diameter holes. An aperture blade can be switched into the optical path 528 to reduce the amount of light transmitted through the lens system 506 to the CCD photo sensor 504. Different apertures 524 are used to control light exposure and to control the focus depth of field. A typical electronic camera that is used for still image reception has one or two aperture blades. Alternatively, the aperture 524 may be composed of a diaphragm with continuously variable aperture hole sizes to supply a greater number of selectable apertures.

[0043] The neutral density filter 526 is an additional blade that can be switched into the optical path 528. The neutral density filter 526 also reduces the amount of light that is transmitted through the lens system 506 to the CCD photo sensor 504. Although an aperture 524 and the neutral density filter 526 are similar in function, the neutral density filter 526 can be used to reduce the amount of light passing through the lens system 506 without affecting the focus depth of field. Usage of an aperture to reduce light to the CCD photo sensor 504 always affects the depth of focus. The neutral density filter 526 can be used in conjunction with the apertures 524 to further reduce the level of light passing to the CCD photo sensor 504.

[0044] The shutter/aperture module 520 is controlled by signals passed from a camera control block (not shown) via solenoids (not shown). Individual blades of the shutter 522, the apertures 524, and the neutral density filter 526 are actuated in and out of the lens optical path 528 by a solenoid. The individual solenoids are driven by a solenoid driver (not shown) which supplies the voltage and current for actuating the blades into position in a timely manner. The solenoid drivers are controlled by signals from a processor (not shown) such as a central processing unit (CPU), a microcontroller, or control logic. The camera control block may be software or firmware that executes on the processor.

[0045] The processor determines relative positioning of the first lens group 508, the second lens group 510, and the third lens group 512, thus controlling zoom and focus functionality. The processor executes application programs that supply control information to a motor driver 534, an executing program code supplying control signals to a DC motor 536 and a stepper motor 538. The DC motor 536 physically controls the position of the first lens group 508 and the second lens group 510 of the lens system 506. The stepper motor 538 physically controls the position of the third lens group 512. The first lens group 508 and the second lens group 510 are held by a lens barrel 540. DC motor 536 is connected to the lens barrel 540 and drives the rotation of the lens barrel 540 via a set of gears (not shown) between the lens barrel 540 and the DC motor 536. As the lens barrel 540 rotates, the positions of the first lens group 508 and the second lens group 510 are adjusted through the operation of cam slots (not shown) inside the lens barrel 540. A lens cam switch 542 is mounted on the lens barrel 540 and sends signal transitions to the processor as the lens barrel 540 rotates through a plurality of zoom positions. In one example, the electronic camera 502 has three zoom positions of wide, tele, and retract. A slider potentiometer 544 is connected to the lens barrel 540. As the lens barrel 540 rotates between the wide and tele zoom positions, the slider potentiometer 544 produces a fine zoom position information. A cam slot 546 in the lens barrel 540 drives the slider potentiometer 544 depending on the position of the wide and tele zoom position. The processor determines the fine zoom position by reading the voltage obtained from the center tap of the slider potentiometer 544 via an analog-to-digital converter (ADC) 548. Fine zoom position values produced by the slider potentiometer 544 are calibrated by recording the slider potentiometer values when the lens cam switch 542 is positioned at the tele and wide positions.

[0046] In the illustrative electronic camera 502, the motor driver 534 sends signals to the stepper motor 538 that is connected to the third lens group 512 by gear reduction 550 and a lead screw 552. The stepper motor 538 receives signals from the processor via the motor driver 534 that determine the position and motion of the third lens group 512. In alternative systems, other types of motors and drive mechanisms can be used to controls lens position adjustment of the third lens group 512. Photo sensors 554 are connected to the motor and drive mechanism for the third lens group 512 to monitor positioning of the third lens group 512. The processor determines the initial position of the third lens group 512 by moving the lens group toward the photo sensor 554 and detecting when flag 562 mounted on the third lens group 512 reaches the photo sensor 554. The position at which the photo sensor 554 detects the flag is a home position. The processor measures the position of the third lens group 512 relative to the home position. The processor tracks the number of steps the stepper motor 538 executes in all moves relative to the home position.

[0047] The motor driver 534 supplies voltage and current to the DC motor 536 and the stepper motor 538, thus determining the position and motion of the first lens group 508 and second lens group 510, and the third lens group 512. The motor driver 534 is controlled by signals from the processor.

[0048] A temperature sensor 560 inside the electronic camera 502 measures temperature and is connected to the processor. The processor includes a processing logic that is capable of adjusting a starting position of the lenses to adjust focus for temperature differences.

[0049] While the invention has been described with reference to various embodiments, it will be understood that these embodiments are illustrative and that the scope of the invention is not limited to them. Many variations, modifications, additions and improvements of the embodiments described are possible. For example, those having ordinary skill in the art will readily implement the steps necessary to provide the structures and methods disclosed herein, and will understand that the process parameters, materials, and dimensions are given by way of example only and can be varied to achieve the desired structure as well as modifications which are within the scope of the invention. Variations and modifications of the embodiments disclosed herein may be made based on the description set forth herein, without departing from the scope and spirit of the invention as set forth in the following claims. For example, one or ordinary skill in the art could similarly apply the first and second quality-of-service techniques to the other interconnect structures described herein.

[0050] In the claims, unless otherwise indicated the article “a” is to refer to “one or more than one”. 

What is claimed is:
 1. An imaging device comprising: an image lens disposed in an optical path; an image sensor coupled to the optical path and capable of detecting illumination passing through the image lens and generating an image signal based on the detected illumination; and a brightness controller coupled along the optical path, the brightness controller capable of executing an auto-focus operation that generates an auto-focus signal based on the image signal, a brightness control operation that controls luminous flux diameter along the optical path, and a light transmittance control operation that controls light transmittance without changing the luminous flux diameter, the auto-focus operation determining a focus condition without changing the luminous flux diameter.
 2. An imaging device according to claim 1 further comprising: a controllable aperture that is controlled to modify the luminous flux diameter.
 3. An imaging device according to claim 1 further comprising: a neutral density filter that can be inserted and removed from the optical path to control light transmittance without changing the luminous flux diameter.
 4. An imaging device according to claim 1 further comprising: a controllable aperture that is controlled to modify the luminous flux diameter; and a neutral density filter that can be inserted and removed from the optical path to control light transmittance without changing the luminous flux diameter, both the controllable aperture and the neutral density filter being disposed along the optical path.
 5. An imaging device according to claim 1 further comprising: a focusing lens disposed in the optical path between the image lens and the image sensor.
 6. An imaging device according to claim 1 wherein: the imaging device is a still image imaging device.
 7. An imaging device according to claim 1 wherein: the auto-focus operation and the light transmittance control operation are performed concurrently.
 8. An imaging device according to claim 1 further comprising: a fixed objective lens disposed along the optical path.
 9. An imaging device according to claim 1 further comprising: a zoom lens disposed along the optical path.
 10. An imaging device according to claim 1 further comprising: a controller; and a control process operational in the controller, the control process including: a processing logic capable of detecting illumination at the image sensor and producing a signal indicative of the amount of light impinging on the image sensor; a processing logic capable of generating an automatic-exposure signal based on the detected illumination level in combination with generation of the auto-focus signal; and a processing logic capable of responding to an increase in detected illumination intensity by controlling light transmittance without changing the luminous flux diameter.
 11. An imaging device according to claim 10 further comprising: a processing logic capable of reducing the detected light to a level within a desired range.
 12. An imaging device according to claim 10 further comprising: a zoom lens disposed in the optical path; a processing logic capable of detecting changes in system setting of the imaging device; and a processing logic responsive to the detected changes in system setting and capable of positioning the zoom lens along the optical path in response to the changed system settings.
 13. An imaging device according to claim 10 further comprising: a processing logic capable of detecting changes in system setting of the imaging device; and a processing logic responsive to the detected changes in system setting and capable of modifying the illumination level of light reaching the image sensor in some circumstances by changing the aperture in other circumstances by inserting the neutral density filter into the optical path.
 14. An imaging device according to claim 10 further comprising: a focusing lens disposed in the optical path; a processing logic capable of detecting changes in system setting of the imaging device; and a processing logic responsive to the detected changes in system setting and capable of modifying the position of the focusing lens and detecting the auto-focus signal at different positions along the optical path.
 15. A control process executable in an imaging device that includes an imaging lens disposed in an optical path, an image sensor coupled to the optical path and capable of detecting illumination passing through the image lens and generating an image signal based on the detected illumination, and a brightness controller coupled along the optical path, the control process comprising: a processing logic capable of executing an auto-focus operation that generates an auto-focus signal based on the image signal; a processing logic capable of executing a brightness control operation that controls luminous flux diameter along the optical path; and a processing logic capable of executing a light transmittance control operation that controls light transmittance without changing the luminous flux diameter, the auto-focus operation determining a focus condition without changing the luminous flux diameter.
 16. A control process according to claim 15 further comprising: a processing logic capable of detecting illumination at the image sensor and producing a signal indicative of the amount of light impinging on the image sensor; a processing logic capable of generating an automatic-exposure signal based on the detected illumination level in combination with generation of the autofocus signal; and a processing logic capable of responding to an increase in detected illumination intensity by controlling light transmittance without changing the luminous flux diameter.
 17. A control process according to claim 15 further comprising: a processing logic capable of reducing the detected light to a level within a desired range.
 18. A control process according to claim 15 further comprising: a zoom lens disposed in the optical path; a processing logic capable of detecting changes in system setting of the imaging device; and a processing logic responsive to the detected changes in system setting and capable of positioning the zoom lens along the optical path in response to the changed system settings.
 19. A control process according to claim 15 further comprising: a processing logic capable of detecting changes in system setting of the imaging device; and a processing logic responsive to the detected changes in system setting and capable of modifying the illumination level of light reaching the image sensor in some circumstances by changing the aperture in other circumstances by inserting the neutral density filter into the optical path.
 20. A control process according to claim 15 further comprising: a focusing lens disposed in the optical path; a processing logic capable of detecting changes in system setting of the imaging device; and a processing logic responsive to the detected changes in system setting and capable of modifying the position of the focusing lens and detecting the auto-focus signal at different positions along the optical path.
 21. A method of controlling brightness in an imaging device including an image lens and an image sensor, the method comprising: detecting illumination passing through the image lens; generating an image signal based on the detected illumination; generating an auto-focus signal based on the image signal; controlling luminous flux diameter along the optical path; and controlling light transmittance without changing the luminous flux diameter, the auto-focus operation determining a focus condition without changing the luminous flux diameter.
 22. A method according to claim 21 further comprising: detecting illumination at the image sensor and producing a signal indicative of the amount of light impinging on the image sensor; generating an automatic-exposure signal based on the detected illumination level in combination with generation of the auto-focus signal; and responding to an increase in detected illumination intensity by controlling light transmittance without changing the luminous flux diameter. 